. >> reporter: he sits in a cell some 500 miles from american shor shores, cal lead shake mohammed, accused mastermind of 9/11 could be closer to residing on the very soil he allegedly conspired to attack. a newly released gao report said military and federal civilian prisons inside the u.s. would need several operational changes if detainees were to be transferred from guantanamo bay, cuba, to the u.s. but to senator dianne feinstein the report shows that if the political will exists, we could finally close guantanamo without imperilling our national security. the report says there are about 2,000 state, federal and local prisons that could be suitable and six military facilities. >> certainly the most likely place the prisoners would be sent would be the maximum security military prison at ft. leavenworth, kansas, that is set up for maximum security. there have never been any escapes. that's the most likely. >> reporter: some civilian supermax facilities inside the u.s. already house well-known convicted terrorists, like khalid sheikh mohammed's nephew, 1993 world trade center bomber ramz